Solvent-free polyurethane resin as well as preparation method and application thereof

Abstract

The invention discloses solvent-free polyurethane resin as well as a preparation method and application thereof. The solvent-free polyurethane resin is prepared from a component A and a component B according to a mass ratio of 100: (15-25), the component A is a carboxyl-terminated polyurethane prepolymer formed by reaction of 70-90 parts by mass of polyester polyol acid, 10-20 parts by mass of diisocyanate and 0.2-1 part by mass of a catalyst; the component B is epoxy resin; wherein the polyester polyol acid is an intermediate with an acid value of 50-80 mgKOH / g and a hydroxyl value of 60-100 mgKOH / g, and the intermediate is obtained by carrying out condensation polymerization on dibasic acid and dihydric alcohol. A component A of a carboxyl-terminated polyurethane prepolymer formed by polyester polyol acid with a specific acid value and a specific hydroxyl value is cross-linked and cured with a component B of epoxy resin, the epoxy resin is embedded in a polyurethane system, and the solvent-free polyurethane resin with excellent comprehensive performance is obtained, has excellent heat resistance, and can be used for preparing the solvent-free polyurethane resin. The material is suitable for the field of products with heat-resistant requirements such as automobile dashboards.

Description

Technical Field

[0001] The present application belongs to the technical field of polyurethane materials, and specifically relates to a solvent-free polyurethane resin and a preparation method and application thereof. Background Art

[0002] Traditional car dashboards are mostly made of materials such as PC and ABS. Although these materials have certain strength and rigidity and can meet the basic structural requirements of car dashboards, they are hard and difficult to create a comfortable driving atmosphere. In contrast, polyurethane materials (PU) have excellent softness and delicate touch, which makes it possible to create soft interiors and become one of the ideal choices for car interior materials.

[0003] However, PU materials have deficiencies in heat resistance. Studies have shown that the mechanical properties and peel strength of PU materials will significantly decrease under high temperature conditions. This defect limits the application of polyurethane in parts that require high heat resistance, such as automotive dashboards.

[0004] Therefore, it is very necessary to research and develop polyurethane materials with excellent heat resistance, so that polyurethane materials can be more widely used in the fields of automotive dashboards, outdoor products, etc. Summary of the invention

[0005] In view of this, the primary purpose of the present application is to provide a solvent-free polyurethane resin, by cross-linking and curing a terminal carboxyl polyurethane prepolymer component A formed by a polyester polyol acid with a specific acid value and a hydroxyl value and a component B of an epoxy resin, embedding the epoxy resin in the polyurethane system, and obtaining a solvent-free polyurethane resin with excellent heat resistance, thereby providing the possibility for the application of polyurethane materials in product fields with heat resistance requirements such as automotive dashboards.

[0006] One aspect of the present application discloses a solvent-free polyurethane resin, wherein the solvent-free polyurethane resin is prepared from component A and component B in a mass ratio of 100:(15-25); The component A is a carboxyl-terminated polyurethane prepolymer formed by the reaction of 70-90 parts by mass of polyester polyol acid, 10-20 parts by mass of diisocyanate and 0.2-1 parts by mass of catalyst; the component B is an epoxy resin; The polyester polyol acid is an intermediate obtained by polycondensation of a dibasic acid and a diol, and has an acid value of 50-80 mgKOH / g and a hydroxyl value of 60-100 mgKOH / g.

[0007] Another aspect of the present application discloses a method for preparing the solvent-free polyurethane resin described above, comprising the following steps: Using dibasic acid and diol as raw materials, polyester polyol acid is prepared through polycondensation reaction; After mixing the polyester polyol acid, diisocyanate and catalyst, heating to 70-100° C. and reacting for 3-5 hours to obtain a carboxyl-terminated polyurethane prepolymer, namely component A; The component A and the component B are uniformly mixed in a mass ratio of 100:(15-25), and reacted at 130-150° C. for 10-15 minutes to prepare a solvent-free polyurethane resin.

[0008] Another aspect of the present application discloses the use of the solvent-free polyurethane resin as described above in the preparation of polyurethane synthetic leather.

[0009] Another aspect of the present application discloses a polyurethane synthetic leather, comprising a polyurethane surface layer and a solvent-free polyurethane layer, wherein the solvent-free polyurethane layer is made of the solvent-free polyurethane resin described above, and the specific process comprises the following steps: The component A and the component B are coated on the polyurethane surface layer in a mass ratio of 100:(15-25), pre-reacted at 100° C. for 70-90 seconds, and bonded to the base fabric; then, the polyurethane synthetic leather is obtained by reaction and curing at 130-150° C.

[0010] Beneficial effects of this application: In this application, a polyester polyol acid with a specific acid value and hydroxyl value is prepared by polycondensation reaction using diol and dibasic acid; it is reacted with diisocyanate to synthesize a carboxyl-terminated polyurethane prepolymer as component A. Since the carboxyl group has a high reactivity, it can undergo a cross-linking and curing reaction with the epoxy resin of component B, and the epoxy resin is embedded in the polyurethane system. This significantly improves the heat resistance of the solvent-free polyurethane resin and the polyurethane synthetic leather.

[0011] After testing, the polyurethane synthetic leather made of this solvent-free polyurethane resin has excellent comprehensive performance; after continuous aging for 200 hours in a high temperature environment of 120°C, the leather surface remains intact, without cracks or stickiness, and the peel strength retention rate is above 80%, with excellent heat resistance. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the implementation methods of the present application. The technical solutions in the implementation methods described below are exemplary and are only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the implementation methods of the present application to obtain other implementation methods without creative work, and these implementation methods are also within the scope of protection of the present application.

[0013] The first aspect of the present application discloses a solvent-free polyurethane resin, wherein the solvent-free polyurethane resin is prepared from component A and component B in a mass ratio of 100:(15-25).

[0014] Component A in this application is a carboxyl-terminated polyurethane prepolymer obtained by reacting a polyester polyol acid with specific acid value and hydroxyl value with a diisocyanate. Utilizing the high reactivity of the carboxyl group, it undergoes a crosslinking and curing reaction with Component B of epoxy resin, embedding the epoxy resin into the polyurethane system to obtain a solvent-free polyurethane resin with significantly improved heat resistance.

[0015] <Component A> Component A described in this application is a carboxyl-terminated polyurethane prepolymer formed by reacting 70 - 90 parts by mass of polyester polyol acid, 10 - 20 parts by mass of diisocyanate, and 0.2 - 1 part by mass of a catalyst.

[0016] Among them, the polyester polyol acid is an intermediate obtained by polycondensing a dibasic acid and a diol, with an acid value of 50 - 80 mgKOH / g and a hydroxyl value of 60 - 100 mgKOH / g.

[0017] In this application, the dibasic acid is an organic dibasic acid, which is a type of organic compound containing two carboxyl groups (—COOH) in its molecular structure. The structural general formula is as follows: HOOC-R1-COOH.

[0018] In this application, R1 is one of —(CH2) n —, —C6H4—, and n is 2 - 8. In some examples, specific instances of the dibasic acid that can be mentioned include, but are not limited to, at least one of succinic acid, adipic acid, sebacic acid, isophthalic acid, and terephthalic acid.

[0019] In this application, the diol is a type of aliphatic organic compound containing two hydroxyl groups (—OH) in its molecular structure and having 2 to 8 carbon atoms. Specific instances that can be mentioned include, but are not limited to, at least one of ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 2 - methyl - 1,3 - propanediol, 1,4 - butanediol, 1,5 - pentanediol, neopentyl glycol, and diethylene glycol.

[0020] In this application, the diisocyanate is any conventional raw material component in the art that can be used to prepare polyurethanes. Specific instances that can be mentioned include, but are not limited to, at least one of 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0021] In this application, the catalyst refers to a reagent used to increase the reaction rate or reaction extent, which can be selected by those skilled in the art according to needs. In some examples, the catalyst is selected from at least one of dimethylaminophenol, triethylamine, benzyldimethylamine, and tetrabutylammonium bromide, but is not limited thereto.

[0022] It is understandable that in the present application, the amounts of the dibasic acid, diol, and catalyst can be adjusted according to the acid value and hydroxyl value of the target polyester polyol acid, and these can all be determined through experiments without special limitations.

[0023] <Component B> In the present application, the Component B is an epoxy resin, and there are no special requirements for its specific type. In some examples, it is preferably a bisphenol A type epoxy resin, such as at least one of E-42, E-44, E-51, and E-55, but not limited thereto.

[0024] The second aspect of the present application provides a method for preparing the solvent-free polyurethane resin, comprising the following steps: Using a dibasic acid and a diol as raw materials, through a polycondensation reaction, a polyester polyol acid is prepared; After mixing the polyester polyol acid, diisocyanate, and catalyst, the temperature is raised to 70-100 °C and reacted for 3-5 hours to obtain a carboxyl-terminated polyurethane prepolymer, i.e., Component A; After uniformly mixing the Component A and Component B according to a mass ratio of 100:(15-25), the mixture is reacted at 130-150 °C for 10-15 minutes to prepare the solvent-free polyurethane resin.

[0025] As described above, in the preparation of the polyester polyol acid, a polycondensation reaction well-known in the art is used. Those skilled in the art can adjust the amounts of the raw material dibasic acid and diol and specific conditions, etc., according to the target acid value and hydroxyl value, without special limitations.

[0026] In some specific examples, the preparation of the polyester polyol acid includes the following steps: Gradually raise the temperature of the dibasic acid and diol to 240 °C under a protective atmosphere for dehydration polycondensation reaction; when the acid value is detected to be 70-100 mg KOH / g, add tetra-isopropyl titanate and continue the reaction, and gradually increase the vacuum degree to 0.095 MPa to obtain a polyester polyol acid with an acid value of 50-80 mg KOH / g and a hydroxyl value of 60-100 mg KOH / g.

[0027] Among them, the dibasic acid, diol, and tetra-isopropyl titanate can be determined by experimental methods as needed. In some examples, the dibasic acid is 170-215 parts by mass, the diol is 120-230 parts by mass, and the tetra-isopropyl titanate is 0.01 part by mass.

[0028] When Component A and Component B are mixed, the carboxyl-terminated group with high reactivity in Component A and Component B being an epoxy resin crosslink and cure, and thus the epoxy resin can be embedded in the polyurethane system to prepare the solvent-free polyurethane resin.

[0029] The third aspect of the present application discloses the use of the solvent-free polyurethane resin in the preparation of polyurethane synthetic leather.

[0030] The fourth aspect of the present application discloses a polyurethane synthetic leather comprising a polyurethane surface layer and a solvent-free polyurethane layer, wherein the solvent-free polyurethane layer is made of the solvent-free polyurethane resin.

[0031] The polyurethane synthetic leather is a conventional composition in the art, including but not limited to a polyurethane surface layer, a solvent-free polyurethane layer and a base fabric layer, etc., which can be specifically configured according to performance requirements. There are no special requirements for the selection of the surface layer and the base fabric layer, etc., and they can be selected accordingly according to the specific application field of the synthetic leather.

[0032] The specific preparation process of the solvent-free polyurethane layer includes the following steps: The component A and the component B are coated on the polyurethane surface layer in a mass ratio of 100:(15-25), pre-reacted at 100° C. for 70-90 seconds, and bonded to the base fabric; then, the polyurethane synthetic leather is obtained by reaction and curing at 130-150° C.

[0033] The polyurethane synthetic leather prepared based on the solvent-free polyurethane resin in this application has excellent comprehensive performance and excellent heat resistance. After high-temperature treatment, the peel strength retention rate is above 80%, which is very suitable for fields such as automotive dashboards and outdoor products that have high requirements for the heat resistance of synthetic leather.

[0034] The following are specific embodiments of the present application. It should be noted that the following specific embodiments are only for illustrative purposes and do not limit the scope of the present application in any way.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0036] In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0037] The raw materials used in the following examples are: HMDI, MDI, and IPDI are diisocyanates produced by Yantai Wanhua Company; tetraisopropyl titanate is the catalyst of Aosjia Material Technology Co., Ltd.; and the surface layer resin LT-95 is a polyurethane resin produced by Hefei Amway Polyurethane New Materials Co., Ltd.

[0038] Example 1 This embodiment discloses a method for preparing a solvent-free polyurethane resin, and the specific steps are as follows: 1. Preparation of polyester polyol acid A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, a N2 inlet tube and an air-cooled condenser was installed in a mantle-type resistance heater, and adipic acid (190 g) and 1,3-propylene glycol (120 g) were added into the four-necked flask; then, the temperature was gradually increased under nitrogen protection to carry out a dehydration polycondensation reaction, and the top temperature of the condenser was controlled to be lower than 100°C during the heating process; when the acid value was detected to be 70 mgKOH / g, a catalyst tetraisopropyl titanate (0.01 g) was added and the reaction was continued for 30 minutes, and then the temperature was gradually increased to 240°C, and the vacuum degree was ≥0.095 MPa, and after removing part of 1,3-propylene glycol, a polyester polyol acid with an acid value of 50 mgKOH / g and a hydroxyl value of 60 mgKOH / g was obtained.

[0039] 2. Preparation of solvent-free polyurethane resin (1) Component A: Take polyester polyol acid (90 g) and add it into a reactor. Then add isophorone diisocyanate (10 g) and catalyst benzyl dimethylamine (0.5 g). Stir and react at 90°C for 5 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0040] (2) Component B: epoxy resin E-55.

[0041] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0042] This embodiment further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0043] Example 2 This embodiment discloses a method for preparing a solvent-free polyurethane resin, and the specific steps are as follows: 1. Preparation of polyester polyol acid A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, a N2 inlet tube and an air-cooled condenser was installed in a mantle-type resistance heater, and sebacic acid (215 g) and 1,5-pentanediol (150 g) were added to the four-necked flask; then, the temperature was gradually increased under nitrogen protection to carry out a dehydration polycondensation reaction, and the top temperature of the condenser was controlled to be lower than 100°C during the heating process; when the acid value was detected to be 80 mgKOH / g, a catalyst tetraisopropyl titanate (0.01 g) was added and the reaction was continued for 30 minutes, and then the temperature was gradually increased to 240°C, and the vacuum degree was ≥0.095 MPa, and after removing part of 1,5-pentanediol, a polyester polyol acid with an acid value of 60 mgKOH / g and a hydroxyl value of 80 mgKOH / g was obtained.

[0044] 2. Preparation of solvent-free polyurethane resin (1) Component A: Take polyester polyol acid (80 g) and add it into a reactor. Then add 4,4'-diphenylmethane diisocyanate (14.5 g) and catalyst triethylamine (0.2 g). Stir and react at 70°C for 3 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0045] (2) Component B: epoxy resin E-51.

[0046] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:19, mixed thoroughly, and reacted at 140° C. for 13 minutes to obtain a solvent-free polyurethane resin.

[0047] This embodiment further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:19, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 80 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 140°C for 13 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0048] Example 3 This embodiment discloses a method for preparing a solvent-free polyurethane resin, and the specific steps are as follows: 1. Preparation of polyester polyol acid A four-necked flask equipped with a magnetic stirrer, a constant pressure burette, a thermometer, a N2 inlet tube and an air-cooled condenser was installed in a mantle-type resistance heater, and isophthalic acid (170 g) and 2-methyl-1,3-propanediol (230 g) were added into the four-necked flask; then, the temperature was gradually increased under nitrogen protection to carry out a dehydration polycondensation reaction, and the top temperature of the condenser was controlled to be lower than 100°C during the heating process; when the acid value was detected to be 100 mgKOH / g, a catalyst tetraisopropyl titanate (0.01 g) was added and the reaction was continued for 30 minutes, and then the temperature was gradually increased to 240°C, and the vacuum degree was ≥0.095 MPa, and after removing part of the 2-methyl-1,3-propanediol, a polyester polyol acid with an acid value of 80 mgKOH / g and a hydroxyl value of 100 mgKOH / g was obtained.

[0049] 2. Preparation of solvent-free polyurethane resin (1) Component A: Add polyester polyol acid (70 g) into a reactor, then add 4,4'-dicyclohexylmethane diisocyanate (20 g) and catalyst tetrabutylammonium bromide (1 g), and stir the reaction at 100°C for 4 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0050] (2) Component B: epoxy resin E-44.

[0051] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:25, mixed thoroughly, and reacted at 150° C. for 10 minutes to obtain a solvent-free polyurethane resin.

[0052] This embodiment further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:80, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 90 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 150°C for 10 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0053] Comparative Example 1 In order to verify the effect of introducing epoxy resin, in this comparative example, the solvent-free polyurethane resin was prepared by curing the hydroxyl-terminated polyurethane prepolymer A component with isocyanate. The other raw materials, and the preparation process of the solvent-free polyurethane resin and synthetic leather were all referred to Example 1. The specific steps are as follows: 1. Preparation of polyester polyols Adipic acid and 1,3-propylene glycol are used to synthesize conventional polyester polyols on the market, with an acid value of 0.3 mgKOH / g and a hydroxyl value of 60 mgKOH / g.

[0054] 2. Preparation of solvent-free polyurethane resin (1) Component A: Take the above polyester polyol (90 g), isophorone diisocyanate (5 g), and catalyst benzyl dimethylamine (0.5 g), and stir and react at 90°C for 5 h to obtain a terminal hydroxyl polyurethane prepolymer, i.e., component A.

[0055] (2) Component B: The polyester polyol (90 g) and isophorone diisocyanate (34 g) were reacted to obtain a terminal isocyanate prepolymer having an isocyanate content of 10%, i.e., component B.

[0056] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:22, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0057] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:22, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0058] Comparative Example 2 In order to compare the acid values ​​of polyester polyol acids, that is, the effect of the amount of epoxy resin added on the heat resistance, polyester polyol acids with different acid values ​​were prepared in this comparative example. Other raw materials, as well as the preparation process of solvent-free polyurethane resin and synthetic leather were all referred to Example 1. The specific steps are as follows: 1. Preparation of polyester polyol acid Referring to Example 1, the acid value of the prepared polyester polyol acid was 120 mgKOH / g and the hydroxyl value was 60 mgKOH / g.

[0059] 2. Preparation of solvent-free polyurethane resin (1) Component A: refer to Example 1.

[0060] (2) Component B: epoxy resin E-55.

[0061] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:35, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0062] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:35, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0063] Comparative Example 3 In order to compare the hydroxyl value of polyester polyol acid, that is, the effect of the content of carbamate group formed by reaction with isocyanate on heat resistance, polyester polyol acids with different hydroxyl groups were prepared in this comparative example, and other raw materials, as well as the preparation process of solvent-free polyurethane resin and synthetic leather were all referred to Example 1, and the specific steps were as follows: 1. Preparation of polyester polyol acid Referring to Example 1, the acid value of the prepared polyester polyol acid was 50 mgKOH / g and the hydroxyl value was 30 mgKOH / g.

[0064] 2. Preparation of solvent-free polyurethane resin (1) Component A: Take the above polyester polyol acid (90 g), isophorone diisocyanate (4 g), and catalyst benzyl dimethylamine (0.5 g), and stir and react at 90°C for 5 h to obtain a carboxyl-terminated polyurethane prepolymer, i.e., component A.

[0065] (2) Component B: epoxy resin E-55.

[0066] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0067] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:15, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0068] Comparative Example 4 In order to compare the performance of the carboxyl / epoxy resin curing system with the hydroxyl / epoxy resin curing system commonly used on the market, the terminal hydroxyl group was used to cure the epoxy resin in this comparative example. The other raw materials, as well as the preparation process of the solvent-free polyurethane resin and the synthetic leather were all referred to Example 1. The specific steps are as follows: 1. Preparation of polyester polyols Adipic acid and 1,3-propylene glycol are used to synthesize conventional polyester polyols on the market, with an acid value of 0.3 mgKOH / g and a hydroxyl value of 60 mgKOH / g.

[0069] 2. Preparation of solvent-free polyurethane resin (1) Component A: Polyester polyol (90 g), isophorone diisocyanate (5 g), and catalyst benzyl dimethylamine (0.5 g) were stirred and reacted at 90°C for 5 h to obtain a hydroxyl-terminated polyurethane prepolymer, i.e., component A.

[0070] (2) Component B: epoxy resin E-55.

[0071] (3) Preparation of solvent-free polyurethane resin: Component A and component B were placed in a low-pressure casting machine at a mass ratio of 100:9, mixed thoroughly, and reacted at 130° C. for 15 minutes to obtain a solvent-free polyurethane resin.

[0072] This comparative example further discloses a polyurethane synthetic leather prepared based on the above solvent-free polyurethane resin, and the specific preparation process is as follows: The surface resin slurry LT-95 was coated on the release paper, and after drying at 130° C. for 2 minutes, a polyurethane surface layer with a thickness of 0.05 mm was obtained; Component A and component B are placed in a low-pressure casting machine at a mass ratio of 100:9, mixed thoroughly and coated on the surface layer with a coating gap of 0.3mm. The mixture is placed in an oven and reacted at 100°C for 70 seconds before being bonded to a base fabric (0.7mm, 270g single-sided special fiber velvet base fabric); the reaction is then continued at 130°C for 15 minutes to allow the solvent-free polyurethane resin to fully cure; after forming, the mixture is rolled up and the release paper is peeled off to obtain polyurethane synthetic leather.

[0073] Performance Testing The polyurethane synthetic leather prepared in Examples 1-3 and Comparative Examples 1-4 was tested for peel strength according to 5.9 standard of GB / T 8949-2008 and 100,000 times of flexure at room temperature and 30,000 times of flexure at -10°C according to QB / T 2714-2018. In addition, in order to further reflect the difference in heat resistance of polyurethane synthetic leather, the polyurethane synthetic leather was placed in a constant temperature oven at 120°C for high temperature aging for 200 hours, and then the peel strength was tested and the peel strength retention rate was calculated. The test results are shown in Table 1.

[0074] Table 1 Test results of polyurethane synthetic leather performance

[0075] Note: Peel strength retention rate in Table 1 = (peel strength before aging - peel strength after aging) / peel strength before aging × 100%.

[0076] As can be seen from the above table, the peel strength of the polyurethane synthetic leather in Examples 1-3 of the present application all reached 90N / 3cm or more, and the flexures at room temperature for 100,000 times and at -10°C for 30,000 times were qualified, with good comprehensive performance. After heat resistance testing, the peel strength retention rate of the synthetic leather in Examples 1-3 was all above 80%, with excellent heat resistance.

[0077] Compared with Example 1, Comparative Example 1 is a polyurethane system without introducing epoxy resin with strong rigidity, and the peel strength is 52N / 3cm, which is relatively low.

[0078] Compared with Example 1, the acid value of the polyester polyol acid in Comparative Example 2 is too high, and more epoxy resin is required for curing. Although higher peel strength and heat resistance can be obtained, the excessive epoxy resin reduces the flexibility of the polymer, and the flexural properties are unqualified.

[0079] Compared with Example 1, the hydroxyl value of the polyester polyol acid in Comparative Example 3 is lower, and the amount of isophorone diisocyanate required for preparing component A is less, resulting in a lower content of urethane groups in the polymer. Therefore, the final peel strength of the synthetic leather is 83N / 3cm, which is lower than that of Example 1.

[0080] Compared with Example 1, Comparative Example 4 uses hydroxyl groups and epoxy resins to form epoxy resin modified polyurethane. Although this approach can also make the synthetic leather obtain good peel strength, the peel strength retention rate is less than 70% after heat resistance testing. This is mainly because the ester bond and other structures formed by the reaction of carboxyl groups and epoxy groups are relatively stable and can maintain the performance of the material at higher temperatures; while the ether bond and other structures formed by the reaction of hydroxyl groups and epoxy groups have certain flexibility, so their heat resistance is poor.

[0081] Based on the above embodiments and performance test results, it can be seen that the solvent-free polyurethane resin provided in the present application has excellent performance, and the prepared solvent-free polyurethane resin and polyurethane synthetic leather have excellent heat resistance, and the peel strength retention rate after high temperature aging treatment at 120°C for 200h is above 80%, and the resin has good flexibility. The solvent-free polyurethane resin can be applied to synthetic leather with high heat resistance requirements such as automotive interiors, dashboards, and outdoor products.

[0082] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A solvent-free polyurethane resin, characterized in that: The solvent-free polyurethane resin is prepared from component A and component B in a mass ratio of 100:(15-25); The component A is a carboxyl-terminated polyurethane prepolymer formed by the reaction of 70-90 parts by mass of polyester polyol acid, 10-20 parts by mass of diisocyanate and 0.2-1 parts by mass of catalyst; the component B is an epoxy resin; The polyester polyol acid is an intermediate obtained by polycondensation of a dibasic acid and a diol, and has an acid value of 50-80 mgKOH / g and a hydroxyl value of 60-100 mgKOH / g.

2. The solvent-free polyurethane resin according to claim 1, characterized in that The diisocyanate is at least one of 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate; And / or, the catalyst is at least one of dimethylaminophenol, triethylamine, benzyldimethylamine, and tetrabutylammonium bromide.

3. The solvent-free polyurethane resin according to claim 1, characterized in that The epoxy resin is bisphenol A type epoxy resin.

4. The solvent-free polyurethane resin according to claim 3, characterized in that The bisphenol A type epoxy resin is at least one of E-42, E-44, E-51 and E-55.

5. The solvent-free polyurethane resin according to claim 1, characterized in that The dibasic acid is at least one of succinic acid, adipic acid, sebacic acid, isophthalic acid and terephthalic acid.

6. The solvent-free polyurethane resin according to claim 1, characterized in that The diol is at least one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, and diethylene glycol.

7. A method for preparing the solvent-free polyurethane resin according to any one of claims 1 to 6, characterized in that: The following steps are involved: Using dibasic acid and diol as raw materials, polyester polyol acid is prepared through polycondensation reaction; After mixing the polyester polyol acid, diisocyanate and catalyst, heating to 70-100° C. and reacting for 3-5 hours to obtain a carboxyl-terminated polyurethane prepolymer, namely component A; The component A and the component B are uniformly mixed in a mass ratio of 100:(15-25), and reacted at 130-150° C. for 10-15 minutes to prepare a solvent-free polyurethane resin.

8. The method according to claim 7, characterized in that The preparation of the polyester polyol acid comprises the following steps: The dibasic acid and diol are gradually heated to 240°C for dehydration and polycondensation reaction under a protective atmosphere; when the acid value is detected to be 70-100 mgKOH / g, tetraisopropyl titanate is added to continue the reaction, and the vacuum degree is gradually increased to 0.095 MPa to obtain a polyester polyol acid with an acid value of 50-80 mgKOH / g and a hydroxyl value of 60-100 mgKOH / g; And / or, the amounts of the raw materials are: 170-215 parts by mass of the dibasic acid, 120-230 parts by mass of the diol, and 0.01 parts by mass of tetraisopropyl titanate.

9. Use of the solvent-free polyurethane resin according to any one of claims 1 to 6 in the preparation of polyurethane synthetic leather.

10. A polyurethane synthetic leather comprising a polyurethane surface layer and a solvent-free polyurethane layer, characterized in that: The solvent-free polyurethane layer is made of the solvent-free polyurethane resin according to any one of claims 1 to 6, and its preparation process comprises the following steps: The component A and the component B are coated on the polyurethane surface layer in a mass ratio of 100:(15-25), pre-reacted at 100° C. for 70-90 seconds, and bonded to the base fabric; then, the polyurethane synthetic leather is obtained by reaction and curing at 130-150° C.

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